For applications that require high power, it’s important to supply that power properly. How can you select the right high power supply? What features should you look for? How do you maximize power density?
In this article, we’ll take a look at how to make the most out of your rack supply.
Choosing the Right Power Supply
Power supplies must provide reliable, stable and clean voltage with minimum noise and ripples. Otherwise, supplies can cause problems including device resets, freezes and more. Choosing a proper power supply is crucial for the best performance of the load.
When choosing a power supply, the first consideration is output power. When determining the output power, future device upgrades and higher power requirements should also be taken into account. Output power is affected by the power supply’s efficiency, which reflects how much input power is dissipated as heat. This factor influences the size of the power supply as well as its cooling methods and input power requirements.
Other important features of power supplies that one should consider are the number of outputs, configuration possibilities and safety requirements regulated for certain applications.
With all these important considerations, power supply manufacturers face the challenge of designing power supplies with an optimal combination of output power, size, cooling and mounting case. The examples below take a look at how this is accomplished with three power supply products: the MEAN WELL DHP-1U rack system and its associated 3200W modules, the DRP-3200 front end rectifier and DBR-3200 battery charger module.
The DHP-1U Rack System
The MEAN WELL DHP-1U is 1U profile 19” rack power system that supports up to four 3,200W modules of either the DRP-3200 front end rectifier or DBR-3200 battery charger. The system has an active current sharing function that enables high output power—up to 12,800W by 1 stack of the 19’’ rack-mountable shelf and 25,600W by 2 stacks. Since it has a universal AC input (90 ~ 264VAC at 47 ~ 63Hz, 127 ~ 370VDC), the DHP-1U can be used in many applications and in many different regions.
The DHP-1U exemplifies many important features of a rack power system.
Hot Swap
Hot swapping means a user can replace or add new modules when the system is online—there’s no need to power off beforehand. For the DHP-1U, this means users can add or swap modules at any time.
Hot swapping is usually achieved using a pre-charged circuit with pins that make contact before the main power supply pins. Such circuits usually use resistors, negative temperature coefficient resistors, and current-limiters to limit the inrush current and prevent damage to the device. A soft start circuit can also be used to provide this type of protection.
Output Power Adjustment
Application requirements can change, and this calls for changes to the output voltage and current of the power supply. This means an important feature of power supplies is the ability to adjust the output voltage and current as needed.
Power supplies with programmable outputs allow users to replace several fixed supplies with a single multi-range supply, therefore saving cost and space. The output voltage of the DHP-1U rack system can be adjusted from 50% to 125% of the nominal output voltage (24V or 48V). The output current can be adjusted from 20% to 100% of the rated current (268A or 532A per rack).
A power supply’s output voltage can be adjusted via a built-in potentiometer. Analog adjustment is stable and reliable, but has limited flexibility. Additionally, the voltage can be trimmed by applying an external voltage (see Figures 2 and 3). In this case, the power supply’s output voltage is controlled by the external voltage input, generally in the range of 1 – 5V.
Remote ON/OFF Control
Rack power systems like the DHP-1U can be turned on and off with a remote ON/OFF function controlled by an electrical signal of dry contact (ON: short, OFF: open). This function is the preferred method over switches to turn ON/OFF high power supplies, because the high inrush current shortens the switch life.
Voltage Drop Compensation
A remote sense function compensates for voltage drop in the load wiring (up to 0.5V in the case of the DHP-1U). Additional voltage sense wires can be used to measure voltage directly on the load. These wires should be twisted in pairs to minimize pick-up noise.
PMBus Communication Interface
Power Management Bus (PMBus) is a commonly used communication protocol for digitally controlling power supplies. Compared to CANbus or Ethernet, PMBus reduces the complexity of power system control because it does not require significant time to develop a protocol stack for use in each specific application.
Power supplies with integrated PMBus enable the end system to monitor and control the power supply's operating parameters (voltage, current and temperature). The DRP-3200 and DBR-3200 support PMBus Rev. 1.1 with a maximum 100kHz bus speed, allowing information reading, status monitoring and output trimming. CANbus is also available as an optional feature.
The many features of the DHP-1U rack system allow it to be adapted to a variety of applications. According to MEAN WELL, the DHP-1U targets applications including distributed power architecture systems, wireless and telecommunication solutions, electric vehicle or marine charger stations, DC UPS or emergency backups, wastewater treatment systems and electrolysis systems.
The DRP-3200 Front End Rectifier
Compatible with the DHP-1U rack system is the MEAN WELL DRP-3200, a 1U low profile power supply with a high power density of up to 37W/inch3. The DRP-3200 is a 3,200W rack-mountable AC/DC power supply with models for 24V and 48V DC output. Each model has a cooling system containing a built-in DC speed controlled fan which allows operating temperatures up to 70°C.The DRP-3200 module characterizes several important power supply features.
High Power Density
Many applications demand high output power, but have limited space available for power supplies. A measure of the relationship between size and power is power density, defined as power per unit volume. The DRP-3200’s 37W/inch3 is among the highest power densities available.
High power density means more power in a smaller space. High power density supplies save space, facilitate easier installation and maintenance and can be placed nearer to loads. Wireless and telecommunication applications require high power density supplies.
High Power Efficiency
Power efficiency is the percentage ratio of total output power to input power:
Power efficiency describes how much input power is lost, primarily as heat. This heat needs to be dissipated properly to avoid damaging the power supply. High efficiency power supplies like the DRP-3200 can stay cooler and require less input power to provide the same output power.
Power efficiency depends on environmental and load conditions (illustrated in Figure 5). Advanced supplies can operate with high efficiency even in the range of 50 – 100% of the nominal load. It is not possible to achieve a power supply efficiency of 100%, but with an advanced design and proper components, high efficiencies are possible. The MEAN WELL DRP-3200, for example, has an efficiency up to 94.5%.
Active PFC
PFC, short for power factor correction (or power factor controller), is a circuit that minimizes the amount of reactive power produced by power supplies. Reactive power is useless, so limiting reactive power reduces costs. PFC improves the power conversion efficiency and also protects the equipment. An active PFC circuit is more efficient than passive PFC, and can automatically detect the AC input voltage in full range.
Active Current Sharing
Power supplies that are connected in parallel can use current sharing to provide more current and power to the load while voltage remains constant. Certain requirements must be met to avoid overloading or damaging power supplies when they operate in parallel. The corresponding control mechanisms need to ensure proportional sharing of the load, and O-Ring diodes are used to isolate the supplies in case of failure. The DRP-3200 supports active current sharing up to 25,600W via two DHP-1U rack shelves.
In addition to these key features, the DRP-3200 supports programmable output voltage, hot swapping, PMBus and CANbus, protections for short circuit/over voltage/over temperature/overload and an alarm signal.
The DBR-3200 Battery Charger
The MEAN WELL DBR-3200 is a 3,200W single output AC/DC front-end charger with a power density of 37W/inch3. The rack-mountable DBR-3200 is designed for charging, backup or constant current source applications, and includes programmable charging curves for different types of lead-acid (flooded, Gel and AGM) and Li-ion (lithium iron and lithium manganese) batteries. The charging voltage and current can be adjusted via potentiometer or PMBus protocol.
Two DBR-3200 models are available: the DBR-3200-24 with 24V and DBR-3200-48 with 48V. The output voltage is adjustable by using the built-in potentiometer or step voltage regulator (SVR) in the range of 23.5 – 30V (for the 24V model) and 47.5 – 58.8V (for the 48V model). Since proper charging is one of the critical factors for long and reliable battery life, the DBR-3200 has various protection mechanisms and a temperature compensation function.
The Charging Curve
Overcharging or overheating a battery causes damages and shortens its lifespan. To avoid this, it is necessary to detect when the full charge capacity is reached and provide overheating protection. Each battery type has its own specific optimal charging curve.
The DBR-3200 charger provides a default charging curve which can be programmed via PMBus. It can enable/disable the charging curve, change to a 2-stage curve and select different curves commonly used for certain battery types.
Figure 7 illustrates the 3-stage charging process. A hybrid charging approach is presented, using a combination of both constant current (CC) and constant voltage (CV) charging methods. The CC charging approach is used in the first stage. When the voltage reaches the maximum safe threshold value, the charging process switches to the CV method. The real charging process is complete when the current levels off or when the full battery capacity is reached. Stage 3 is the float operation mode, where the voltage on the battery is maintained to allow a full battery charge without any damage.
The charging parameters for both DBR-3200 models (24V and 48V) and corresponding battery types are defined in the table below:
Note that the DBR-3200 needs to be configurated with the recommended battery capacity provided by the battery manufacturer. In case of a lower battery capacity, a lower charging current must also be set.
According to MEAN WELL, the DBR-3200 is best suited for applications including large scale DC UPS emergency backup systems, marine battery charger modules, electric vehicle charging stations, wastewater treatment systems and electrolysis systems.
For more information on rack supply systems, power supplies and battery charger modules, the MEAN WELL products discussed in this article are available here: the DHP-1U (rack system), DRP-3200 (front end rectifier), and DBR-3200 (battery charger).